P202A: reductant tank-heater openness is evaluated when heating starts

P202A concerns the reductant tank-heater control circuit being open. Audi's CPNB chart evaluates conductance at the start of heating and lists a value at or below 0.10 reciprocal ohm. The timing and quantity are both part of the criterion.

Conductance is not resistance

The table uses inverse ohms, not an ohm reading. As diagnostic interpretation, copying 0.10 into a resistance test as though the units were interchangeable would be incorrect. Conductance expresses the ability of the path to carry current; the applicable repair information determines how the controller's criterion relates to a workshop measurement.

The start-of-heating condition also means that an unrelated reading taken at another operating stage may not reproduce the monitor event.

Keep the heater identity clear

This row concerns the tank heater. The same book describes other reductant heating circuits separately, so the named circuit should be confirmed before applying a measurement. The chart gives no universal connector arrangement or complete disassembly procedure. A useful diagnosis establishes why the relevant heating path appears open under its commanded conditions. These criteria are scoped to the CPNB section of Audi's 2014 A6/S6 book and are not a blanket instruction to replace the reductant tank.

Source: Audi 2014 A6/S6 Quick Reference Specification Book.